For a long time, wastepaper has been a source of fiber material used in paper making. To reclaim the fiber from the wastepaper, it is necessary to remove the ink from pulp fiber when processing the wastepaper for reuse. During reclamation of wastepaper, deinking methods include converting the wastepaper to pulp by macerating pieces of paper in water with agitation. The aqueous pulp slurry is made alkaline and a deinking agent is added. The physical action of pulping the paper in the alkaline aqueous medium causes the ink to separate from the paper pulp fiber. The deinking agent keeps the deinked particles dispersed in the aqueous medium so that the resultant mixture may be subsequently treated to separate the suspended ink from the paper pulp fibers.
Traditionally, fiber from waste paper was employed only in the manufacture of low-grade paper products. With today's emphasis on environmental clean-up, however, more and more reclaimed fiber is being employed in paper making as a result of which methods to upgrade the quality of the reclaimed product are continually being sought.
In the past, the reclaimed paper came from newspapers and books, which are printed with oil-based inks. Such inks are removed from paper by saponification reactions. Several patents serve as background with regard to removal of ink from conventionally printed paper, such as newsprint and books. As can be seen, most of these background patents require a surfactant to keep the deinked particles dispersed throughout the slurry of pulp.
Many of these background patents show the addition of a multi-component agent during pulping. For instance, U.S. Pat. No. 4,959,123, issued Sep. 25, 1990 to Lehmann et al., shows the use of a four-component additive of (a) alkali metal silicate, (b) oxidative bleach, (c) dispersant, and (d) either (i) higher fatty acid or (ii) resonic acid during the pulping operation. U.S. Pat. No. 4,964,949, issued Oct. 23, 1990 to Hamaguchi et al., shows the use of a two-component additive of (a) the reaction product of alkylene oxide+mixture of (i) natural fat or oil and (ii) polyhydric alcohol and (b) alkylene oxide adduct of (i) higher alcohol, (ii) sulphate, or (iii) higher fatty acid in the pulping operation. U.S. Pat. No. 5,158,697, issued Oct. 27, 1992 to Kawamori et al., shows the addition of the reaction product of alkylene oxide+one of (a) C.sub.16-20 fatty acid, (b) C.sub.17-28 ester, or (c) dicarboxylic acid or ester that contains cyclohexene during the pulping operation. U.S. Pat. No. 4,231,841, issued Nov. 4, 1980 to Calmanti et al , shows the addition of a five-component mixture containing surfactant wherein the five components are (a) salt of a fatty acid, (b) nonionic ethoxylated or propoxylated surfactant, (c) anionic surfactant that is a sulfonate, (d) sodium-carboxymethyl-cellulose, +(e) alkaline inorganic salt during the pulping operation.
Other background patents showing the addition of a multi-component agent during pulping are U.S. Pat. No. 4,162,186, issued Jul. 24, 1979 to Wood et al., and U.S. Pat. No. 4,666,558, issued May 19, 1987 to Wood et al., each of which shows the addition of a similar two-component mixture of surfactants during the pulping operation. The two components disclosed in '186 are (a) water soluble nonionic surfactant from C.sub.9-15 ethoxylated aliphatic alcohol with 7-15 ethyleneoxy units per mole of alcohol+(b) oil soluble nonionic surfactant from C.sub.9-15 ethoxylated aliphatic alcohol with 0.5-3.5 ethyleneoxy units per mole of alcohol, whereas the two components disclosed in '558 are (a) C.sub.9-16 alkanol ethoxylate with 6.5- 20 oxyethylene units per ethoxylated molecule+(b) oil soluble C.sub.9-16 alkanol ethoxylate with 0.5-3.5 oxyethylene units per ethoxylate molecule.
Like the two Wood et al. patents, there are two Illingworth patents that are also background showing the addition of a two-component mixture of surfactants during pulping. More particularly, U.S. Pat. No. 3,932,206, issued Jan. 13, 1976 to Illingworth et al., shows the addition of a two-component surfactant mixture of (a) ethoxylated mono-ol+(b) ethoxylated di-ol where the hydroxy groups in the di-ol are present on adjacent non-terminal carbon atoms during the pulping operation. U.S. Pat. No. 3,392,083, issued Jul. 9, 1968 to Illingworth, shows the addition of a two-component mixture of (a) nonionic surfactant having a phenol group+(b) polyol during the pulping operation.
Additionally as background, it is noted that U.S. Pat. No. 4,935,096, issued Jun. 19, 1990 to Gallagher, shows the use of an ionic surfactant during the pulping operation. U.S. Pat. No. 5,013,456, issued May 7, 1991 to St. John et al., involves de-inking of printed paper that was derived from paper that had already been recycled, and uses a water soluble polymer as a coagulant during the pulping operation. The preferred coagulant is polydiallyl dimethyl ammonium chloride polymer containing 5-30 mol. % of water soluble anionic monomer such as acrylic acid in the polymer chain, specifically a copolymer of polydiallyl dimethyl ammonium chloride+ acrylic acid. U.S. Pat. No. 5,073,234, issued Dec. 7, 1991 to Mollet et al., shows the use of a resin precursor which is cured while it is in the pulp during the pulping operation. The resin precursor is a mixture of fluid prepolymers having .gtoreq.2 reactive functional groups per molecule, and a cross-linking agent is added to cross-link the prepolymers thereby effecting curing to make a polymer in the pulp, and then the polymer collects the deinked particles. U.S. Pat. No. 3,069,307, issued Dec. 18, 1962 to Boaz et al., shows the addition of ethoxylated phenolic compound as a surfactant during the pulping operation, and specifically state that the pulp must be caustic free.
Lastly as background, U.S. Pat. No. 2,005,742, an old patent issued Jun. 25, 1935 to Hines, discloses a fundamental pulping operation involving shredding newspaper with caustic soda, lime, and sodium silicate, which causes the deinked particles to flocculate at the top of the slurry so that they can be removed by floating them away.
With the increased use, however, over the last few decades of photocopiers, computers, and facsimiles, the source of more and more of reclaimed paper is xerographically printed paper. In contrast to conventionally printed paper, such as newspapers and books, xerographically printed paper uses a special type of ink which contains toners to help the ink stick to the paper. The toners are typically made of a polymer such as polyvinyl butyral, polyacrylate, polystyrene, styrene-acrylate copolymer, and the like. Thus, such toner-containing inks are very difficult to remove from the xerographically printed paper so that the paper may be recycled. A general discussion of xerographic inks and the special problems in deinking paper printed with such inks since they use polymers as toners is in Quick and Hodgson, "Xerography Deinking--A Fundamental Approach", Tappi Journal, Vol. 69, No. 3, pp. 102-106 (March, 1986).
More particularly, it is noted that the following five patents involve processes for the deinking of xerographically printed paper.
During deinking of xerographically printed paper, U.S. Pat. No. 4,276,118, issued Jun. 30, 1981 to Quick, shows the addition of a long chain alcohol to the pulping operation, whereby the long chain alcohol agglomerates the deinked particles. Also added during the pulping operation are polystyrene beads to act as what Quick designates a collector for collecting the particles. The polystyrene beads are preferred to be small prills of less than 5 mm in diameter and to have a solubility parameter similar to that of the toner used in the ink. The particles cling to the polystyrene collector, and then the prills with the particles stuck to them are removed from the slurry. Quick is silent as to how these prills containing the particles are supposed to the removed from the slurry.
During deinking of xerographically printed paper, U.S. Pat. No. 4,561,933, issued Dec. 31, 1985 to Wood et al., also shows the addition of a long chain alcohol during the pulping operation to agglomerate deinked particles. Additionally added during the pulping operation is nonionic surfactant. The long chain alcohol in combination with the nonionic surfactant causes the particles to form a suspension so that the particles stay dispersed throughout the slurry. The dispersed particles are then removed by either washing or flotation.
U.S. Pat. No. 5,141,598, issued Aug. 25, 1992 to Richman et al., requires three components to be added to the aqueous slurry of xerographically printed paper during the pulping process. These three components are: (a) aliphatic petroleum distillates, (b) alkylphenoxypoly-(ethyleneoxy) ethanol, and (c) ethoxylated polyoxypropylene glycol, wherein the hydrophile/lipophile balance of (b)+(c).ltoreq.10 and the weight ratio of (a):(b):(c) is approximately 6:1:3. Component (a) acts as a solvent and the combination of components (b)+(c) acts as a surfactant. The specification U.S. Pat. No. 5,141,598 to Richman et al. mentions separating the deinked particles from the slurry by flotation.
U.S. Pat. No. 5,102,500, issued Apr. 4, 1993 to Darlington, shows the addition of a polymer having a glass transition temperature of 20.degree.-70.degree. C., together with a substituted polyethylene oxide, to the aqueous slurry of xerographically printed paper during the pulping operation. The specification of U.S. Pat. No. 5,102,500 to Darlington mentions separating the deinked particles from the pulp-containing aqueous medium by conventional centrifugation, filtration, flotation, sedimentation, decantation, or washing. It is noted that the polymers used are either polystyrene or styrene-carboxylic acid copolymer, which are like the polystyrene prills employed as a collector in U.S. Pat. No. 4,276,118 to Quick discussed above.
U.S. Pat. No. 3,635,789, issued Jan. 18, 1972 to Green, involves making a slurry of paper pulp from xerographic printing in which the little deinked particles float to the top and also benzene is added to the slurry. Benzene has a lower specific gravity than water and thus floats on the top of the slurry, thereby collecting the particles. Lastly, the benzene layer containing the particles is skimmed off.